1. Field of the Invention
This invention relates to an electronic device using a carbon fiber reinforced resin for its casing.
This application claims priority of Japanese Patent Application No.2003-283228, filed on Jul. 30, 2003, the entirety of which is incorporated by reference herein.
2. Description of the Related Art
Generally, in electronic devices such as digital still cameras, digital video cameras, radio receivers, television receivers, personal computers and personal digital assistants (PDAs), sufficient measures to prevent electromagnetic interruption (EMI) and to strengthen immunity must be taken so that radiation of unwanted electromagnetic waves (unwanted radiation) and malfunction due to the influence of external electromagnetic waves can be prevented when electronic components housed in the casings operate.
For example, in a digital video camera, unwanted electromagnetic noise is generated from a charge couple device (CCD), which is an image pickup device, and a printed circuit board having a driving control circuit of a rotary head unit mounted thereon. To prevent leakage of unwanted radiation noise generated from the CCD and the printed circuit board, the CCD and the printed circuit board are covered with shield cases made of a conductive metal, respectively, and the shield cases are grounded. Since a head amplifier for processing and amplifying minute video signals need be protected from external electromagnetic waves, it is shielded by a shield plate. However, each of these shielding measures complicates the device structure and makes its assembly difficult.
Thus, in such an electronic device, its outer casing is made of an electromagnetic absorbing material such as ceramics or magnesium alloy so that the outer casing absorbs unwanted electromagnetic waves generated from internal electronic components and external electromagnetic waves. In this manner, occurrence of noise and electromagnetic interruption is prevented and the function the device is stabilized without taking measures to shield the electronic components (see, for example, Patent Reference 1).
However, the metal casing made of magnesium alloy or the like needs secondary processing such as surface polishing and anticorrosive treatment in order to reduce roughness of the surface. Therefore, there are problems of low productivity and very high cost.
As for a portable electronic device, in order to reduce size and weight, it is proposed that a casing formed by injection-molding a glass fiber reinforced resin, carbon fiber reinforced resin or the like having small thickness, light weight, high strength and high rigidity is used, other than the above-described metal casing made of magnesium alloy or the like.
However, in the casing made of a glass fiber reinforced resin or carbon fiber reinforced resin, the glass fiber or carbon fiber is exposed on the surface and the surface becomes rough, or the unevenness of the fibers appears clearly and the appearance of the casing is deteriorated. Although secondary processing such as surface coating and polishing is carried out, the coating is stripped off the part where the glass fiber or carbon fiber is exposed. Moreover, the carbon fiber breaking out from the surface of the casing may contaminate the periphery and occurrence of a short circuit due to the carbon fiber exposed from the surface of the casing may be anticipated.
Patent Reference 1: Japanese Patent Gazette No. H07-052798